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11.
过冷层状云中飞机播云有效区域的模拟研究 总被引：8，自引：2，他引：8
根据飞机人工增雨作业个例 ,利用层状云中催化剂输送扩散的三维时变模式 ,对过冷层状云中播云产生的有效区域、催化剂水平输送和扩散速率等进行了模拟研究。结果表明 :(1)飞机播云 4 5min线长 32 7km ,投影有效面积和有效体积在播云刚结束时 (5 0分 )达到极大 ,其值分别为 70 7km2 和 2 98.0km3 ,有效扩展宽度和厚度为 2 .5 1km和 0 .4 2km ;(2 )有效作用时段为 2 0～ 80min ,其间的投影有效面积平均值为 5 13.3km2 ,平均有效扩展宽度和厚度分别为 2 .4 1km和 0 .4 5km ;(3)在扩散作用下 ,投影有效面积和有效体积先随时间不断增加 ,达到极值后逐渐减小 ,播云结束 (5 5分 )后 ,云中的有效区域消失 ,其间的投影有效面积平均值为 389.7km2 ,平均有效扩展宽度和厚度分别为 2 .34km和 0 .4 4km ;(4)云中催化剂水平输送 1h的平均值达到 6 5km ,仅与风场有关。催化剂扩散速率 1h平均为 0 .82m/s,与风、温、湍流有关 ;(5 )在飞机增雨作业时 ,飞行方案的设计必须是严格科学的 ,以便进一步提高人工增雨的实效 相似文献
12.
Dynamical Nighttime Fog/Low Stratus Detection Based on Meteosat SEVIRI Data: A Feasibility Study 总被引：1，自引：0，他引：1
Automated detection of fog and low stratus in nighttime satellite data has been implemented on the basis of numerous satellite
systems in past decades. Commonly, differences in small-droplet emissivities at 11μm and 3.9μm are utilized. With Meteosat SEVIRI, however, this method cannot be applied with a fixed threshold due to instrument design:
The 3.9μm band is exceptionally wide and overlaps with the 4μm CO2 absorption band. Therefore, the emissivity difference varies with the length of the slant atmospheric column between sensor
and object. To account for this effect, the new technique presented in this paper is based on the dynamical extraction of
emissivity difference thresholds for different satellite viewing zenith angles. In this way, varying concentrations of CO2 and column depths are accounted for. The new scheme is exemplified in a plausibility study and shown to provide reliable
results. 相似文献
13.
It is essential to learn the temporal and spatial concentration distributions and variations of seeding agents in cloud seeding
of precipitation enhancement. A three–dimensional puff trajectory model incorporating a mesoscale nonhydrostatic model has
been formulated, and is applied to simulating the transporting and diffusive characteristics of multiple line sources of seeding
agents within super–cooled stratus. Several important factors are taken into consideration that affect the diffusion of seeding
materials such as effects of topography and vertical wind shear, temporal and spatial variation of seeding parameters and
wet deposition. The particles of seeding agents are assumed to be almost inert, they have no interaction with the particles
of the cloud or precipitation except that they are washed out by precipitation. The model validity is demonstrated by the
analyses and comparisons of model results, and checked by the sensitivity experiments of diffusive coefficients and atmospheric
stratification. The advantage of this model includes not only its exact reflection of heterogeneity and unsteadiness of background
fields, but also its good simulation of transport and diffusion of multiple line sources.
The horizontal diffusion rate and the horizontal transport distance have been proposed that they usually were difficult to
obtain in other models. In this simulation the horizontal diffusion rate is 0.82 m s−1 for average of one hour, and the horizontal average transport distance reaches 65 km after 1 h, which are closely related
to the background fields. 相似文献
14.
A stratus-sea fog event that occurred over the Yellow and East China Seas on 3 June 2011 is investigated using observa-tions and a numerical model, with a focus on the effects of background circulation and Sea Surface Temperature Front (SSTF) on the transition of stratus into sea fog. Southerly winds of a synoptic high-pressure circulation transport water vapor to the Yellow Sea, creating conditions favorable for sea fog/stratus formation. The subsidence from the high-pressure contributes to the temperature inversion at the top of the stratus. The SSTF forces a secondary circulation within the ABL (Atmospheric Boundary Layer), the sink-ing branch of which on the cold flank of SSTF helps lower the stratus layer further to reach the sea surface. The cooling effect over the cold sea surface counteracts the adiabatic warming induced by subsidence. The secondary circulation becomes weak and the fog patches are shrunk heavily with the smoothed SSTF. A conceptual model is proposed for the transition of stratus into sea fog over the Yellow and East China Seas. Finally, the analyses suggest that sea fog frequency will probably decrease due to the weakened SSTF and the reduced subsidence of secondary circulation under global warming. 相似文献
15.
16.
分析了１９９１－１９９３年人工降水期间共１３个架次粒子测量系统（ＰＭＳ）获取的冰、雪粒子的二维图像资料，分析了雪粒子的形态特征，重点分析霰粒子出现的频率及其尺度谱特征；并利用霰粒子的直径大小，在一定的假设条件下，估算了观测高度以上云中所包含的过冷水的累积含量；借以了解飞行层以上的的人工降水潜力状况。初步分析结果表明，不少架次的飞行过程都出现有持续时间不等的霰粒子，估算出的最大积分过冷水含水量为１３ 相似文献
17.
机载微波辐射计测云中液态含水量 总被引：5，自引：0，他引：5
文中介绍了 2 0 0 1～ 2 0 0 2年 4～ 7月吉林省人工增雨期间 ,在中国首次进行的机载对空微波辐射计外场飞行观测试验。观测结果表明 ,仪器可以灵敏地探测出层状云中垂直路径积分云液态水和过冷水含量及其变化 ,揭示了在层状云中嵌入的对流区中有丰富的垂直积分过冷水含量 ,量级可达 10 3 g/m2 。与地面雷达PPI回波强度呈正相关。本文还根据飞机上升 (或下降 )过程的探测数据 ,给出了水平均匀的层状云液态含水量的垂直廓线的实例 ,并进一步讨论了这种方法的应用前景。 相似文献
18.
选取成都信息工程学院气象观测场LNM激光雨滴谱仪获得的2009—2011年175次降水过程的观测资料,依据产生降水云的性质进行统计分类,基于微物理特征参量讨论了成都地区积云、积层混合云以及层状云降水雨滴谱的总体特征,同时结合3个典型个例的微结构参量进行对比分析。结果表明:成都地区积云降水和积层混合云降水的雨滴谱比层状云宽且雨滴数密度比层状云多,特别是在大雨滴和甚小雨滴部分;4种反映雨滴谱特性的特征直径从大到小依次为积云降水、积层混合云降水、层状云降水;成都地区层状云降水的雨强主要来自于小雨滴,而积云降水和积层混合云降水的雨强主要来自于大雨滴;雨强取决于大雨滴的数量,小雨滴贡献率与雨强呈负相关,中数体积直径对雨强变化有一定指示作用。对成都地区雨滴谱特征的研究,有利于进一步了解该地区降水的微物理特性及成雨机制,为降水数值预报工作积累资料和经验。 相似文献
19.
The Chinese east coastal areas and marginal seas are foggy regions.The development of effective forecasting methodsrests upon a comprehensive knowledge of the fog phenomena.This study provides new observations associated with the sea fogsover the northwestern Yellow Sea by means of L-band radar soundings with a high vertical resolution of 30 m.The monthly tem-perature lapse rate,the Richardson Numbers,and the humidity show obvious seasonal variations in the lower level of the planetaryboundary layer (PBL) that are related to the onset,peak and end of the Yellow Sea fog season.The typical pattern of stratification forthe sea fog season in the northwestern Yellow Sea is that a stable layer of about 400 m thick caps a 150 m conditionally unstable layer.Besides,the differences between fogs and stratus clouds in terms of humidity,turbulence and temperature are analyzed,which is ofsignificance for sea fog forecast and detection by satellites.The thickness of the sea fogs varies in different stages of the fog season,and is associated with the temperature inversion.The numerical simulation proves that the seasonal variations obtained by the radarwell represent the situations over the Yellow Sea. 相似文献
20.
During February 1992, a series of relatively warm storms passed eastward across southern California, yielding intense precipitation that triggered widespread mass movement, flooding, property damage, and loss of life. These storms were triggered by an intense low pressure system (976 mb) off northern California which deepened as its eastward progress was initially blocked by a high pressure ridge (1040 mb) across western North America. Between February 10 and 13, large areas of Ventura and Los Angeles counties experienced cumulative precipitation of 200–400 mm with intensities reaching 40–50 mm hr-1. Mass movement, mainly as soil slips that transformed downslope into debris flows, occurred where cumulative precipitation exceeded 300 mm and when sustained intensities exceeded 25 mm hr-1. Stream response was rapid, particularly in urban areas where impermeable surfaces and storm drains fed concrete stream channels. The canalized upper Los Angeles River and Arroyo Simi exceeded all previous discharges for over 43 and 36 years of record, respectively. Other streams, from the large Santa Clara River to modest Malibu Creek, yielded recurrence intervals for the peak discharge of between 8 and 24 years, but the rapidity of flooding everywhere was remarkable. Whereas main trunk streams, canalized or not, responded predictably, the storm series emphasized the problems of poorly controlled development of potentially unstable hillsides and floodable lowlands and indicated a need to reassess the assumptions upon which such development is permitted. [Key words: climatology, cyclonic storm, geomorphology, mass movement, flooding, California]. 相似文献